Question marks on map

[Koro]

I'm seeing question marks on certain maps. When I go there, I don't see anything I can pick up and interact with. Am I missing something?

[Silyon]

Usually yes. Each of the question marks is an object of interest, usually involving a new character unlock. Some of them, like the one in the Bone Zone, can move about so make sure to triple-check your map and try to avoid weapons that clutter the screen with too many particles to see.

[Nibbie]

Also sometimes the question mark isn't centered on the thing, try looking around the general area rather than directly on top of the mark.

[bugbear]

I found a question mark in the Bat Country with three A B C buttons near it, but I couldn't figure out what they do. =(

[-=|Markus|=-]

https://primagames.com/tips/how-to-discover-the-source-of-the-roaring-thunder-on-the-tiny-bridge-in-vampire-survivors

The functions of these buttons are not going to impact your gameplay. They will just have a visual effect on the stage looks:

A toggles the visibility of the entire stage. When you turn the stage off, you’ll basically just have a pastel-colored plane to walk on.
B toggles the background chessboard graphics.
C toggles the sphere graphic in the background that reminds us of the old-school Sonic levels where you are running around a sphere.